The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Substrate processing systems may be used to perform deposition and/or etching of film on a substrate such as a semiconductor wafer. Substrate processing systems typically include one or more processing chambers each with a substrate support such as a pedestal, an electrostatic chuck, a plate, etc. A transport handling chamber including one or more robots may be used to receive the substrates and to move the substrates to the one or more processing chambers for processing. After processing, the one or more robots move the substrates from the processing chamber back to the cassette.
For example only, in a chemical vapor deposition (CVD) process, a gas mixture including one or more precursors may be introduced into the processing chamber to deposit a film on the substrate or to etch the substrate. In some processes, radio frequency (RF) plasma may be used to activate chemical reactions. Some chemical reactions that happen in the gas phase generate particles that may remain in the processing chamber after processing is completed. In addition to the particles created during processing, particles may also reach the processing chamber or transport handling chamber due to dusted upstream parts, chamber leak events, contamination that occurs when replacing parts, and/or contamination that occurs during maintenance.
Some processes require substrates to meet or exceed a particle count standard or the substrates need to be rejected. For example only, one industry standard for particles on a substrate is <50 particles that have a size >45 nm. As the minimum feature sizes continue to shrink, the industry standards for particles will be specified for smaller particle sizes.
Currently, light scattering may be used to detect on-wafer particles. Synthetic particles of a known size, shape, and composition are systematically placed on a substrate. The substrate is rotated and bombarded with a single wavelength of light. The reflected light is measured and stored. The process is repeated for a range of synthetic particles sizes of a known shape and composition. This process establishes a correlation between the particle size and intensity of scattered light.
Later, substrates with particles of unknown size, shape, and composition are rotated and the scattered light is compared to the known scattering intensities. Interpolation and extrapolation may be used to correlate the scattering light intensity with particle size. The particle sizes that can be measured are constrained by the wavelength of the light source for scattering. The size of the particles that are detected is a function of the wavelength. Smaller wavelengths of light can detect smaller particles. As the wavelengths of light decrease below the vacuum ultraviolet limit (<200 nm), several issues arise that make the light scattering method more difficult. For example below 200 nm, air begins to ionize. This decreases the intensity of the light and invokes interactions that decrease the signal to noise ratio. The light scattering method has been used to detect particles down to 26 nm.